Brake Pedal Return Question

[Whaanga]

I brought my 73 bus out of winter storage yesterday and glad to say it started up with a little coaxing and is now running well. However, I am experiencing some brake pedal issues that I have not seen before. On occasion, after the first pedal application when braking, the pedal returns slowly to its normal position.

What is the process/mechanics that return the pedal back to its 'ready' position?

Even though it's still cold here in Western NY, it seems logical that brakes are not effect by temperature so I'm trying figure why I am experiencing slow brake pedal return on occasion. I checked the fluid and the reservoir is full and there are no visible leaks at the M/C or wheel cylinders.


I have been dealing with a brake servo issue as see here:

https://www.thesamba.com/vw/forum/viewtopic.php?t=687495&highlight=

and wonder if my brake pedal return issues may be related to vacuum or the servo issue itself.

As always, any help/input is much appreciated.

Thanks, Jeff
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Late 1973 Bay w/a transplanted 914 Engine

[raygreenwood]

Its a spring.

So if the spring is not returning the pedal.....there are a few items that could be,slowing its,return.

1. Just poor greasing of pivot points on the pedal and pushrod or in the brake booster.
2. Sticking compensation port flap valves on the pistons. If you do not bleed your brakes on a regular basis.....say every other year no matter the miles....most expecially on a vehicle that is stored with no running in the winter.....this can be an issue.

3. Old master cylinder seals that are finally starting to disintegrate.....not that common....but if the master cylinder is old....it can just as easily be rust dragging on the seals. Ray

[Whaanga]

Thanks Ray,

The brakes have been bled several times in the last 18 months - and the fluid is fresh. Will investigate the items you mention.

The brake pedal is always good and the brakes are very responsive on the first application when stopping: it's the second application where the issue will manifest itself - and as said before, it's intermittent. So as long as I don't let off the pedal on the first application, I have good responsive brakes. But intermittent brakes are not a safe bet so I have to track this down.
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Late 1973 Bay w/a transplanted 914 Engine

[raygreenwood]

[Whaanga]

The master cylinder's age is unknown to me - but from the photos, it looks old. Can these be rebuilt or refurbished or is it best to replace? You also mentioned pivot points, are these points of movement in the mechanism that can be clean and greased?

Thanks, Jeff

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Late 1973 Bay w/a transplanted 914 Engine

[raygreenwood]

Yes....they can be rebuilt....if you can get a good kit....and if the cylinder has no rusty pits more than about .003" deep.

If you are mechanically inclined...its really not hard at all to rebuild a master cylinder.

BUT....the cost for doing it yourself is sometimes pretty close to just buying a new one. The only risks of buying a new one are...can you get a good quality part.
And because of that last comment....if you are more inclined to keep a good rebuildable German master cylinder core ...for both quality and collect-ability sake (which I agree with)....the real key is being able to tell when the cylinder is beyond use/repiar or not.

To do a master cylinder rebuild PROPERLY...PROPERLY....to make sure its done right, safely and is worth the hassle...requires only 3 things really.

1. You need to be good enough with tools to inspect it and measure it. So it takes maybe 3 minutes to pull one apart. You want to wash it out with hot water and oil it lightly...for the moment...so you can inspect it without it rusting further.

If its heavily scored....which happens only from debris and grit getting into the brake fluid...because the pistons do not actually touch the bore....or if its heavily rust pitted....as long as the scores and pits are not more than about .003" deep...you can reuse it after a light honing....a very light honing.

The the key part of inspecting is measuring the bore. Yes...you can get away with a good caliper near the top of the cylinder but a better way is with a telescopic gauge and a micrometer. The BEST way is with a small bore micrometer or dial gauge...but thats an expensive piece of kit.

The key you are looking for is that when the bore of the MC becomes more than .005" larger than the piston heads....its too large to safely rebuild.

The typical factory range of tolerance is .002" to .005" larger than the bore. The problem is that a great many of the MC's come from the factory already at .003" to .004". Still plenty in spec....but not really rebuildable if you have to hone one to get rid of pits and scoring in the .003" range.

2. If the bore is still sized right and not excessively pitted or scored....You need to buy a very fine grit flexhone. 800 grit is ideal. 600 grit is fine. It will run you about $35.

The object is NOT to hone the bore out oversized. Its to put a slight tooth on it to allow a fine lubricating film of fluid for the seal cups to operate without any actual abrasion and to deburr any rough spots.

3. If you are going to assemble, install and bleed immediately...you can use brake fluid for a lube. If you are going to shelve it for over a week....buy some DEDICATED brake assembly lubricant.

Rock auto has kits for about $42
https://www.rockauto.com/en/moreinfo.php?pk=309990&cc=1441346&jsn=403

So between lube, a hone and a kit...you are probably at about $110 and some work with shipping. But you keep a nice OEM cylinder in play for another decade or so.

But you have to have the time on your hands to be able to strip the MC, inspect and measure to decide whether its worth ordering a kit....or if its too far gone and you should just order a new complete cylinder.

Rebuilding a master cylinder is about 1.5-2.0 hours max including cleaning but not including external paint.

As for what Rockauto stocks in new cylinders....I would go with the Centric. I have seen a lot of crap from IAP.
https://www.rockauto.com/en/catalog/volkswagen,197...inder,1836

Here is a stock ATE for $179
http://www.busdepot.com/211611021aa

About the same price at Cip1 for an ATE.
http://www2.cip1.com/ProductDetails.asp?ProductCode=C24-211-611-021-AAGR

https://www.thesamba.com/vw/forum/viewtopic.php?t=679160

Here is a basic how to write on on rebuilding and MC problems. By the way...DO NOT buy any NOS brake MC's. New German or new centric or even new raybestos....but if you opt for a remanufactured cylinder...do it yourself.

Ray

[Whaanga]

Thank You Ray - this is very helpful and detailed information.
I'm comfortable doing the rebuild work but I'm inexperienced in terms of determining whether or not the MC has enough life left for a rebuild.
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Late 1973 Bay w/a transplanted 914 Engine

[busdaddy]

What made that lighter colored mark on the bottom of the booster? If it's hit something and is bent that will definitely cause a binding pedal.
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[Whaanga]

That mark is from me and a wire brush in my drill. I was trying to get a sense of how much rust/corrosion was/is on the servo.
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Late 1973 Bay w/a transplanted 914 Engine

[vwwestyman]

I had this on my '73 a while back. It was something in the linkage, where the rod goes into the booster.

I used some silicone spray lube a few times over a few days to let it get worked in there. I used the little tube that comes on the can to get it under the rubber boot.That took care of the problem and have had no issues since.

Something like that might be worth a try before tearing the master cylinder all apart.
_________________
Dave Cook

President, Wild Westerner Club

1978 Champagne Edition Westy, repowered to '97 Jetta TDI
1973 Wild Westerner
My Thing

[raygreenwood]

Oh....sorry...forgot to answer the other question. Your brake pedal is on a pivot pin....and it has a pushrod attached to it that pushes on the pistons. It is held to the pedal with a pin and circlip. Its a rotating joint. If its rusty it can drag.

Measuring is pretty easy. For a lot of precison work....I would not recomend these. But for occasional work they do fine

https://m.harborfreight.com/6-piece-telescoping-ga...20provided

Just like any other tool....really fine ones will cost. A set of Starret are $275 and worth every penny. Id you can afford a little more for something you WILL use again.....these are worthy.

http://www.wttool.com/index/page/product/product_i...G3EALw_wcB

But you need a 1" micrometer to work with them. If you are really careful and have a GOOD electronic or dial caliper you can get away with it for this one task. When you get to that point I will he happy to explain the use of both the telescopic gauges and the caliper or micrometer here.

The object if you buy telescopic gauges is to clamp the cylinder to sometjing so you do not have to hold it...vise C-clamp etc.....measure the piston heads.....and write that down. Then manually open the micrometer or caliper to .005" larger than what it reads....and take a bore meazurement with the telescopic gauge and fit it in to see the differene.

Be patient and take your time and take about 20 measurements over about,10 minutes.....just to get the hang of using this gauge..... practice. You will be fine.

So how do you know if the pits are over. 003"....well Im used to doing it.....but do the measurements. If you have room enough left to hone.....then do a quick hone. It takes less than a minute.
Then measure again. For example if by honing you oversized the bore by .001"....and ots still in good enough spec.....and the pits have devreased in diameter or width by half.....you know they were only about .002" deep. Small pits of .003" deep the cups can seal when they run over them.
Ray

[SGKent]

1) in front of the brake booster there is a rod that goes up to the brake pedal. Spray the pivot point with some penetrating oil or even just oil the pivot.

2) Spray the brake cluster are with some oil or even WD40. White lithium grease etc.

3) look at your floor mat and be sure it isn't rubbing on the brake. If it does then spray a little silicone lube on it.

I haven't seen a cast iron master or slave cylinder worth rebuilding in 40 years. The rust pits them so bad that by the time one knows it the pits are too deep. Last one I did was on a Sunnen hone in 1976 in So Cal when the bus had something like 50,000 miles on it. I think we used to redo the Fiat ones but they were aluminum and even that was a crap shoot because of electrolysis.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[Zed999]

Have you looked to see if the pedal return spring is broken? They do break.
Or pedal partly seized on shaft?
In the uk with our salty winter roads, both these are common.

[SGKent]

to anyone thinking of rebuilding their master or slave cylinders after reading this thread, just be prepared to throw your money away. If the pits in the master are deep enough to cause the seals to leak, or to tear them up, the pits are usually too deep to hone out. FACT

Rebuilding a caliper is different because the pits are usually in an area that the seal doesn't come in contact with.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[Whaanga]

I'm glad to report that, thanks to the good advice here, I cleaned and lubed the contact points as suggested and the pedal comes right back as designed.

I still am having an occasional issue with too much vacuum so that the pedal travels too far on a second application. If I release the pedal and re-apply, it has the correct amount of resistance and travel. In either instance, I have full brake stopping capability. Am working on the servo itself as it's missing the air vent on the rod side. I also need to double check the hoses as I don't think the ones currently installed are actually vacuum hoses but intended for fuel or brake use.

Per the debate between Steve and Ray, I don't have enough experience to comment but appreciate both points of view. If I need to replace the MC, will probably look for a new unit since I simply could not make a well-informed and accurate assessment of its condition.

Thanks, Jeff
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Late 1973 Bay w/a transplanted 914 Engine

[SGKent]